1. Field of the Invention
The invention relates to an image reading apparatus which is used for, for example, a scanner, a facsimile, or the like.
2. Related Background Art
Hitherto, as one of image reading apparatuses, a contact type multi-chip image sensor constructed by a light source, a short focal point image pickup element array, and a plurality of line sensors is known. FIGS. 1 to 3 show an example of such an image reading apparatus. A transparent glass plate 201 which is in contact with an original surface is attached onto the upper surface of a frame 200. An emission light 212 of an LED 211 attached onto an LED board 210 provided in the frame 200 is reflected by the original surface which is in contact with the upper surface of the transparent glass plate 201. An optical system 209 for transmitting a reflection light 213 from the original surface to be read and a sensor array 1 provided on a board 19 in correspondence to the optical system 209 are provided in the frame 200. As an optical system, the foregoing short focal point image pickup element array represented by, for example, xe2x80x9cCellhock lens array (trade name)xe2x80x9d (made by Nippon Sheet Glass Co., Ltd.) is used.
As shown in FIG. 3, the sensor array 1 is constructed by arranging a plurality of line sensors 2-1, 2-2, . . . , and 2-15 in a line on the board 19 and is covered with a protecting film 206. In the contact type multi-chip image sensor, since the reflection light from the original is formed as an image onto the sensor array at an equal magnification and is read in principle, a length of sensor array 1 needs to be set to a value corresponding to only the width of original to be read.
Therefore, the necessary length of sensor array 1 changes depending on the size of original to be read and the number of line sensors constructing the sensor array 1 also changes. The case of reading the original of the A3 size will now be considered as an example. Assuming that a length of one line sensor is equal to 20 mm, it is sufficient to construct the sensor array by 15 line sensors.
The board 19 is supported onto a bottom plate 205 which is in engagement with the frame 200 and is connected to a flexible board 203 through a flexible wiring 208. A connector 202 for input and output of a power source, a control signal, and the like is provided on the flexible board 203 and is attached to the frame 200 by a screw 207.
The operation of the contact type multi-chip image sensor will now be described with reference to FIG. 4 showing wirings on the board and FIG. 5 showing a timing chart. The operations of the plurality of line sensors 2-1, 2-2, . . . , and 2-15 arranged in a line on the board 19 are started by a start pulse xcfx86SP and a shift register 36-1 starts the operation. Now, assuming that the number of photosensitive (pixel) elements arranged in each line sensor is equal to 316, the shift register 36-1 which started the operation generates signals for sequentially making switches 32-1-1, 32-1-2, . . . , and 32-1-316 conductive, thereby allowing the signals accumulated in photosensitive elements 31-1-1, 31-1-2, . . . , and 31-1-316 to be transferred to an output line 33-1. While the reading operation of the line sensor 2-1 is being performed, a switch 35-1 is conducting by a control signal xcfx86sw1, so that the signals transferred to the output line 33-1 are transmitted through a buffer amplifier 34-1 to a common output terminal Vout on the board 19.
An output signal xcfx86end1 at the final stage of the shift register 36-1 in the line sensor 2-1 is connected by the wiring on the board 19 and becomes a start pulse xcfx86st2 of the line sensor 2-2. After completion of the reading of the signal of the line sensor 2-1, the reading operation of the line sensor 2-2 is started. In a manner similar to the line sensor 2-1, a shift register 36-2 starts the operation and sequentially makes switches 32-2-1, 32-2-2, . . . , and 32-2-316 conductive, thereby allowing signals accumulated in photosensitive elements 31-2-1, 31-2-2, . . . , and 31-2-316 to be transferred to an output line 33-2.
While the reading operation of the line sensor 2-2 is being performed, a switch 35-2 is conducting by a control signal xcfx86sw2, thereby allowing the signals transferred to the output line 33-2 to be transmitted to the common output terminal Vout through a buffer amplifier 34-2.
Similarly, an output signal xcfx86end2 at the final stage of the shift register 36-2 in the line sensor 2-2 is connected by the wiring on the board 19 and becomes a start pulse xcfx86st3 of the line sensor 2-3. The reading operation of the line sensor 2-3 is executed subsequent to the line sensor 2-2. In a manner similar to the above, signals of the line sensors 2-4 to 2-15 are also sequentially read out by a similar procedure.
As mentioned above, the sensor array 1 constructed by a plurality of line sensors 2-1, 2-2, . . . , and 2-15 functions as one image sensor and sequentially generates the signals of all of the photosensitive elements to the common output terminal Vout.
After completion of the reading of the image data of one line, the contact type multi-chip image sensor is moved in the sub scanning direction (direction perpendicular to the arranging direction of the plurality of line sensors) by a distance corresponding to one line and reads the next line. By repeating the above operation a number of times corresponding to the original size, an image of the entire original is completely read out by using the contact type multi-chip image sensor.
In the above conventional apparatus, however, since the signals of all of the sensor chips are sequentially outputted to one output line, it takes a time to obtain the signals of one line. Although a request such that the user wants to read the original in a short time is increasing more and more in recent years, if the user tries to output the signal at a high speed in such a construction, the circuit to read out the signals from the photosensitive elements, buffer amplifiers, and the like have to be constructed so as to cope with a further higher band, thereby causing complication of a circuit construction and a manufacturing process. This inevitably results in an increase in costs and becomes a large problem, on the other hand, since the reduction of the costs is also an important object. Further, the realization of the high output speed in the conventional apparatus also causes a problem such that not only does the complexity of the circuit design increase but the number of development elements, such as analog signal processes of the generated signals and the like, increase also so that development time increases.
An object of the invention is to provide an image reading apparatus which can read an image at a high quality in a short time.
Another object of the invention is to provide an image reading apparatus which can read an image at a high quality and at a high speed.
Still another object of the invention is to provide an image reading apparatus which can read an image at a high quality by means of a simple construction.
Yet another object of the invention is to provide an image reading apparatus which can read an image at a high quality and with low cost.
To accomplish the above objects, according to an embodiment of the invention, there is provided an image reading apparatus in which a plurality of line sensors each for converting an image pickup light into an electric signal are arranged in the longitudinal direction, comprising: driving means for driving the plurality of line sensors; and switching means for switching a first operation to simultaneously drive the plurality of line sensors by the driving means and to output signals of the line sensors in parallel and a second operation to sequentially drive the plurality of line sensors by said driving means and to sequentially output the signals of the line sensors.
With this construction, the image reading apparatus which can output the signals by a simple construction can be provided.
According to another embodiment of the invention, there is provided an image reading apparatus in which a plurality of line sensors each for converting an image pickup light into an electric signal are arranged in the longitudinal direction, comprising: driving means for driving the plurality of line sensors by a same frequency; and control means for controlling so that a drive timing of at least one of the plurality of line sensors by the driving means is shifted from drive timings of the other line sensors by a predetermined period shorter than a reading period from photosensitive elements on the line sensor.
With the above construction, an image reading apparatus having low cost and high performance in which the signals of the line sensors can be outputted at a high speed by a simple construction can be provided.
According to yet another embodiment of the invention, there is provided an image reading apparatus in which a plurality of line sensors each for converting an image pickup light into an electric signal are arranged in the longitudinal direction, comprising: driving means for driving the plurality of line sensors; memory means for storing output signals of the plurality of line sensors driven by the driving means; and control means for controlling so as to simultaneously execute a writing operation of a signal into a first memory area in the memory means and a reading operation of a signal from a second memory area different from the first memory area.
With the above construction, an image reading apparatus which can perform the image reading operation in a short time without realizing a high output speed in the line sensor can be provided.
The above and other objects and features of the present invention will become apparent from the following detailed description and the appended claims with reference to the accompanying drawings.